Banks' online security is getting worse as they rush to offer services online, according to new research.

This year's Annual Security Report from NTA Monitor, a security testing firm, found that 20 percent more security vulnerabilities turned up in the infrastructures of banks, building societies and other financial institutions compared with last year's report. The survey covers networks, applications and systems.

By comparison, a month ago NTA reported that the security of UK organisations in general improved year-on-year. Thirty-two percent of UK organisations tested had critical vulnerabilities that are widely known and exploited, compared to 61 percent in 2006.

Meanwhile, financial organisations tested positive for an average of three more vulnerabilities in the 2007 survey, NTA said.

A common category was buffer overflows in Bind running on DNS servers, which could allow an attacker access to the server.

Another common problem was expired SSL certificates, which force users to acknowledge that they know the certificate is invalid before they can access the site.

NTA technical director Roy Hills said the increase in security problems is due to growing pressure on financial organisations to go online. "Whilst this extra accessibility is of benefit to many customers, at the same time it can increase the exposure to external attacks," he said in a statement.

Among NTA's recommendations are to ensure SSL certificates are always renewed on time, to change default settings on Apache, in order to avoid denial of service attacks, and to keep up to date with patches.